The invention relates to an apparatus for producing plastics material pre-forms from a thermoplastic plastics material according to the preamble of claim 1. In addition, the invention relates to a method for producing plastics material pre-forms from a thermoplastic plastics material.
Various apparatus and methods for producing plastics material pre-forms from thermoplastic plastics materials are known from the prior art. On the one hand there is the injection moulding method, in which after drying with dry air which has a dew point of between approximately 243 K and approximately 233 K, the plastics material granulate is melted at a temperature of between approximately 513 K and approximately 573 K in an injection unit and is introduced under pressure into the respective cavity for the plastics material pre-forms. The apparatus or tools respectively for producing plastics material pre-forms of this type are as a rule provided with hot runner tools, in which case the melted plastics material is distributed by way of a hot runner distributor to individual cavities in order to produce a plurality of plastics material pre-forms during one moulding cycle.
Customary numbers of cavities in this case are in the range of from 72 to 96. Accordingly, both the machines to be used and the hot runner distributors are relatively large and complex. The hot runner distributors are usually provided with a needle shut-off system or the like, so that the individual ducts of the hot runner distributor can be closed at the end of the process cycle. In this way, no melted plastics material can escape from them when the cavities now filled with melted plastics material are moved away from the hot runner distributor in order to cool the plastics material pre-forms and new empty cavities are positioned on the hot runner distributor for filling with melted plastics material. An apparatus of this type and a method of this type are known for example from DE 2 154 441 A1. A problem in this case, however, is that the melted plastics material cannot be conveyed in a continuous manner, and this results in an inefficient production process, in particular with respect to the energy balance, since the melted plastics material has to be tempered accordingly until it is introduced into the corresponding cavity, so that it may retain its flow properties for introduction into the cavity.
On the other hand, although an apparatus by which the melted plastics material can be conveyed in a continuous manner is known from U.S. Pat. No. 4,828,778 A, it is nevertheless not possible to observe present-day standards with respect to hygiene and cleanness since the extruder nozzle there is at a distance from the carrier element there which contains the cavities for the plastics material pre-forms and which moves the cavities past the extruder nozzle for filling with melted plastics material. The use of an apparatus of this type or of a method of this type respectively in the production of plastics material pre-forms for the foodstuffs or pharmaceuticals industry is questionable since the plastics material can be contaminated over the distance between the extruder nozzle and the cavities if the extrusion is not carried out in ultra-clean or sterile rooms.
In addition, a method known as “Exjection” and a corresponding apparatus are disclosed in WO 2006/045720 A1. In the case of very long parts and very high flow path ratios (quotient of flow path and wall thickness) the problem arises in injection moulding that the plastics material melt freezes (i.e. the free cross-section freezes up from the edge) and the plastics material part to be moulded cannot be shaped out. This problem is solved conventionally in that use is made of a so-called cascade injection moulding. In this case a plurality of injection points, which are used in sequence, are provided along the flow path. As a result, the production process of the long part is subdivided into shorter portions.
The “Exjection” method makes a continuous method from this clock-timed method. A continuous melt duct which is moved past the point of the melt supply replaces the relatively large number of the injection points in the case of cascade injection casting. This method can also be used for the production of parts which are designed almost like profiles capable of being extruded but which have interruptions (for example cable ducts). Nevertheless, on the basis of the method disclosed in WO 2006/045720 A1 and the apparatus there it is not possible to produce plastics material pre-forms.
The object of the invention is therefore to make available an apparatus and a method for producing plastics material pre-forms from a thermoplastic plastics material, in which the melted plastics material can be conveyed into the cavities in a continuous manner in order to form the plastics material pre-forms, while at the same time preventing contamination of the melted plastics material.
This object is attained by an apparatus with the features of claim 1 and by a method with the features of claim 12. Advantageous embodiments of the invention are set out in the sub-claims.